Quick Answer
The answer is that the API Gateway execution role lacks the lambda:InvokeFunction permission. This is the most likely cause of an AccessDeniedException when invoking Lambda from API Gateway because API Gateway operates under an IAM execution role that must explicitly grant it permission to call the Lambda function, separate from any resource-based policy on the Lambda side. Even if the Lambda resource-based policy allows API Gateway to invoke it, the API Gateway service itself still needs its own role to authorize the invocation request. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding of the dual authorization model: both the caller’s IAM role and the resource’s policy must grant permission. A common trap is assuming a resource-based policy alone is sufficient, but API Gateway always needs its execution role to include lambda:InvokeFunction. Memory tip: think of it as a two-key lock—the Lambda policy is one key, but API Gateway’s execution role is the second key you cannot forget.
This DVA-C02 practice question tests your understanding of troubleshooting and optimization. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A developer receives an AccessDeniedException when trying to invoke a Lambda function from an Amazon API Gateway REST API. The Lambda resource-based policy allows API Gateway. What is the most likely issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
The Lambda function is in a VPC without a NAT gateway.
Why wrong: VPC affects network, not IAM.
The Lambda function concurrency limit is exceeded.
Why wrong: Concurrency exceeded causes throttling, not access denied.
The API Gateway execution role lacks lambda:InvokeFunction permission.
Execution role needs invoke permission.
API Gateway caching is enabled, returning stale responses.
Why wrong: Caching does not cause access denied.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The API Gateway execution role lacks lambda:InvokeFunction permission.
Option C is correct because when API Gateway invokes a Lambda function, it must have the `lambda:InvokeFunction` permission. Even if the Lambda resource-based policy grants API Gateway access, the API Gateway execution role must also explicitly allow the `lambda:InvokeFunction` action. Without this permission, API Gateway cannot invoke the function, resulting in an AccessDeniedException.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
The Lambda function is in a VPC without a NAT gateway.
Why it's wrong here
VPC affects network, not IAM.
The Lambda function concurrency limit is exceeded.
Why it's wrong here
Concurrency exceeded causes throttling, not access denied.
The API Gateway execution role lacks lambda:InvokeFunction permission.
Why this is correct
Execution role needs invoke permission.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
API Gateway caching is enabled, returning stale responses.
Why it's wrong here
Caching does not cause access denied.
Common exam traps
The trap here is that candidates often assume the Lambda resource-based policy alone is sufficient, overlooking that API Gateway's execution role must also grant the `lambda:InvokeFunction` permission, which is a separate IAM authorization layer.
Detailed technical explanation
Under the hood, API Gateway uses an execution role (an IAM role) to assume permissions for invoking backend integrations. The `lambda:InvokeFunction` permission must be attached to this role, not just the Lambda resource-based policy. A common real-world scenario is when the execution role is missing the `lambda:InvokeFunction` action or the resource ARN is incorrectly scoped, leading to an AccessDeniedException even if the resource-based policy appears correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
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FAQ
Troubleshooting and Optimization — This question tests Troubleshooting and Optimization — Read the scenario before looking for a memorised answer..
The correct answer is: The API Gateway execution role lacks lambda:InvokeFunction permission. — Option C is correct because when API Gateway invokes a Lambda function, it must have the `lambda:InvokeFunction` permission. Even if the Lambda resource-based policy grants API Gateway access, the API Gateway execution role must also explicitly allow the `lambda:InvokeFunction` action. Without this permission, API Gateway cannot invoke the function, resulting in an AccessDeniedException.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This DVA-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DVA-C02 exam.
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